As a prior-art conveyance system for an object to be conveyed, there is a generally known system for conveying an object to be conveyed to a container mounted on a chassis of a trailer (see Patent Literature 1, for example). Patent Literature 1 discloses a stage device arranged behind the chassis of the trailer positioned in a predetermined position determined in advance. This stage device includes a conveyance vehicle on which the object to be conveyed is placed and conveyed, a stage on which the conveyance vehicle travels, lock pins to be inserted into insertion holes formed in corner fittings of the container, and a lifting/lowering device for lifting and lowering the lock pins. By inserting the lock pins into the insertion holes in the corner fittings of the container mounted on the chassis and lifting the lock pins, the container is raised to align a floor face of the stage and a floor face of the container substantially at the same height and to keep the container on the level. At the same time, the conveyance vehicle on which the object to be conveyed is placed is lifted by air and pushed by a person to convey the heavy object into the container.